Cell Reproduction
Cell reproduction is an important of human physiology. In this case, an expectant woman is presenting with a cut that is slow to heal. In human beings, there are two distinct types of cell reproduction processes responsible for cell division, meiosis and mitosis. Mitosis is a continuous process that goes in in somatic cells responsible for tissue growth, healing and repair. In comparison, meiosis is responsible for the formation of sexual gametes in human which later fuse during fertilization to form an oocyte which later form a fetus. Both reproductive cells are vital for normal body physiology.
Mitosis
Hall (2016) describes that through mitotic division, a single somatic cell produces two replicates of itself with the same number of chromosomes as the parent cell. These two cells are known as daughter cells. The process goes through five distinct phases. Before division can occur, the genetic material within the nucleus of the cell has to be duplicated for the resulting daughter cells to be genetic replication of the parent cell during the interphase stage. Thus, the strands of the Deoxyribonucleic Acid (DNA) within the chromosomes are replicated by the enzyme DNA polymerase. The new strands are joined by the DNA ligase enzyme. The whole process lasts for about 8 hours just before the cell division starts. Hall adds that the new and old DNA strands remain bonded to each other by weak Hydrogen bonds before they are uncoiled periodically by special enzymes. For the short pause between DNA replication and mitotic division, there is proofreading of the new DNA material. During this process, the polymerase and ligase enzymes go over the new DNA strands to eliminate any defects and repair any damages. It is important to note that if any defects in the nucleotide sequence the new cells are said to be mutated. This would later result in abnormal cellular function due to altered protein production which is unwanted. Nevertheless, the transcription process in humans is rarely ever prone to mistakes.
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Cells which are abnormal are usually marked for cell death. With exception of gametes, all human cells contain 46 chromosomes which are arranged in pairs. After the DNA duplication, the chromosomes are duplicated in their entirety. The duplicate and the old chromosomes remain attached via an organelle known as the centromere, forming chromatids, until it is time for division. The cell also contains the mitotic apparatus which consists of the cylindrical centrioles, surrounding spindle between them and an aster which is responsible for separating the chromatids. The first mitotic stage is the prophase during which the chromosomes within the nucleus become condensed. And the spindle fibers between the centrioles continue to divide. The division progresses into the prometaphase stage during which the aster enters the nucleus membrane and its tubules attach to the centromere at which they polarize the chromatids at opposite ends. The third stage is the metaphase stage during which the spindles of the mitotic apparatus line up the chromatids along a middle metaphase plate that runs down the middle of the cell in readiness for division. The division progresses to anaphase where the chromatids are separated from one another through the centromere to form 46 chromosomes on either side. The final stage is the telophase whereby the two separate DNA materials are further polarized from each other. New DNA membranes formed from the cellular endoplasmic reticulum envelop each of the separated material and the mitotic material is resolved. Contractile proteins are responsible for dividing the cell into two daughter cells with exact number of chromosomes as the original parent cells. Hall (2016) concludes that this is the process of division for somatic cells.
Meiosis
Barett et al., (2019) illustrate that eukaryotes also undergo a second type of cell division that is meiosis. Through this process, a single cell divides to form four cells with half the number of chromosomes as the parent cells, also known as haploid cells. In humans, this is the process through which gametes, both male and female are formed which is essential for reproduction. During fertilization, the two gametes from both genders fuse to form an oocyte which later develops into a fetus. Before meiosis, the cell undergoes replication of genetic material similar to the interphase stage of mitosis. However, meiosis is divided into two divisions, I and II. In prophase I, the chromosomes that have been duplicated in interphase start to condense as in mitotic prophase. However, they are also matched to form homologous pairs which carry the same genetic material. This is essential for the exchange of genetic material in a process known crossing over. Since meiosis produces gametes that would later form another human being, this ensures that diversity of the human race is maintained.
The chromosome pairs remain attached to each other by the chiasmata until the genetic exchange process is complete. The division process then progresses to metaphase I where the homologue pairs are lined up along the metaphase plate that runs down the cell in a randomized manner which ensure genetic material is randomly distributed to either side of the plate. In Anaphase I, the chromosomes are polarized from one another by mitotic spindles. Meiosis I is finalized in telophase I when the chromosomes reach the opposite ends of the cell and the cell divides to form two cells with 26 chromosomes. The division then moves into Meiosis II. Here, there is no duplication of DNA material but rather, two cells from meiosis II are farther divided to form haploid cells with half the number of chromosomes as the parent cells. Meiosis II begins with prophase II in which the chromosomes condense and spindle fibers begin to divide. The division moves to metaphase II where the chromosomes line up along the middle metaphase plate. In anaphase II, the chromatids pairs are separated from one another by the mitotic microtubules. Finally in telophase II, nuclear membrane envelope the genetic material on either side of the cell before the cell splits into haploid cells containing half the number of chromosomes as the parent cell. Barrett et al., (2019) conclude that this is how gametes are formed in humans.
Overview of Mitosis and Meiosis
Both mitosis and meiosis are vital parts of human physiology. However, Clift and Schuh (2013) note that both are limited in their respective function. Mitosis is necessary for normal tissue growth, regeneration and healing which maintain the integrity of body tissues. However, mitosis produces the same cells and shows little variation.
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